Exemplary embodiments of the invention relate to a method and device for generating electrical energy.
A device for generating current for units provided in a motor vehicle, in particular for a washing system, is disclosed in German patent document DE 41 18 979 A1. The washing system includes a reservoir for holding fluid which via at least one supply line is in connection with a nozzle having an outlet opening. The fluid present in the system is heatable via a heating device, composed of at least one thermogenerator situated in the region of the exhaust manifold.
German patent document DE 10 2007 005 520 A1 discloses a vehicle having a thermoelectric generator. The vehicle includes a heat-releasing component and the thermoelectric generator, which has a heat-absorbing element thermally coupled to the heat-releasing component, and which generates electrical energy based on the temperature gradient between the heat-absorbing element and a heat sink. The thermoelectric generator is situated directly at the heat-releasing component, and is thus connected thereto in a thermally conductive manner.
German patent document DE 10 2006 057 662 A1 discloses a vehicle having a thermoelectric generator. The vehicle includes an internal combustion engine and the thermoelectric generator, which has at least one element that absorbs heat from a heat source and at least one element that releases heat to a heat sink, and two electrical connections via which the thermoelectric generator may deliver electrical energy. A heat exchanger is provided which has the heating elements thermally connected to the at least one heat-absorbing element of the thermoelectric generator, and cooling elements thermally connected to the at least one heat-releasing element of the thermoelectric generator. Exhaust gas flows through and around the heating elements, which are situated in the exhaust duct of the internal combustion engine.
Japanese patent document JP 2008022688 A describes a system for determining a maximum performance point of a thermoelectric generator and control of the thermoelectric generator into the maximum performance point. In the process, an internal resistance of the thermoelectric generator is measured. In addition, a resistance is determined by measuring an input current and voltage during operation. The control is carried out in such a way that the value of the load resistance corresponds to the value of the internal resistance of the thermoelectric generator.
German patent document DE 32 45 866 A1 discloses a system and method for regulating alternative energy sources to maximum power. An adaptor device between the energy source and the consumer is regulated in such a way that the power delivered in each case at the highest and the lowest voltage value is determined from current and voltage fluctuations and stored. Based on the stored values, a difference is continuously formed whose value and polarity indicate the magnitude and the direction of the instantaneous operating point from the maximum performance point. At the same time, this information is used to form a signal for the command variable for the adaptor device.
Exemplary embodiments of the present invention are directed to an improved method and device for generating electrical energy, and use of a method and/or a device for generating electrical energy.
In a method for generating electrical energy by means of a thermoelectric generator, which is coupled to at least one electrical consumer and has a plurality of thermoelectric modules, according to the invention module open-circuit voltages of the modules are determined, and those modules for which a sum of their module open-circuit voltages attains twice a predefined generator output voltage with the smallest possible deviation are determined and electrically connected to one another in series.
“A plurality of components” is understood to mean a number of components that is at least two.
According to the invention, a device for generating electrical energy for carrying out the method includes a thermoelectric generator which is coupled to at least one electrical consumer and has a plurality of thermoelectric modules.
According to the invention, module open-circuit voltages of the modules are determinable, and those modules for which a sum of their module open-circuit voltages attains twice a predefined generator output voltage with the smallest possible deviation are determinable and electrically connectable to one another in series. The method and the device are usable in a motor vehicle.
By means of the method and the device, the thermoelectric generator or its modules may be easily and efficiently operated at a maximum performance point or at least close to the maximum performance point. Module output voltages correspond to the respective modules when the modules are operated at the maximum performance point, which is one-half the particular module open-circuit voltage. The predefined generator output voltage corresponds to an input voltage of the electrical consumer, for example an electrical system of the motor vehicle. When the modules are connected to one another according to the invention and connected to the vehicle electrical system, comprising at least one voltage-stabilizing component (battery, generator, or capacitor) and electrical consumers, since the electrical load is large with respect to the generator and therefore is a stronger partner with respect to the thermoelectric generator, the generator output voltage of the thermoelectric generator adapts to the voltage of the vehicle electrical system; i.e., the module output voltages of the modules then correspond to one-half or at least close to one-half the particular module open-circuit voltage, and thus to the voltage at the maximum performance point or at least close to the respective performance point of the particular module.
The module output voltages of the modules are thus automatically brought to the output voltages at their respective maximum performance point or at least close to their respective maximum performance point, and the modules are thus operated at their respective maximum performance point or at least close to their respective maximum performance point. The sum of the output voltages of the modules electrically connected to one another in series then corresponds to the generator output voltage of the thermoelectric generator and to the input voltage of the electrical consumer.
If the sum of the module open-circuit voltages corresponded to exactly twice the predefined generator output voltage before the modules were connected, the modules are now operated exactly at their respective maximum performance point, and the sum of the output voltages of the modules at their respective maximum performance point corresponds exactly to the generator output voltage and to the input voltage of the electrical consumer. If the sum of the module open-circuit voltages differed from twice the predefined generator output voltage with the smallest possible deviation before the modules were connected, now the modules are not operated exactly at their respective maximum performance point, but are operated at least close to their respective maximum performance point with the smallest possible deviation therefrom. If the modules had been operated at their respective maximum performance point, the sum of the output voltages of the modules would then be close to the actual generator output voltage and to the input voltage of the electrical consumer with the smallest possible deviation therefrom.
A d.c.-d.c. converter is not necessary for carrying out the method. In addition, the method and the device allow dynamic control and/or regulation of the thermoelectric generator. This is very advantageous in particular when the thermoelectric generator is used in a motor vehicle, since temperature differences between the hot side and the cold side continually change. The thermoelectric generator is thermally coupled via its hot side or via the hot side of its modules to an exhaust system of the motor vehicle, for example. In addition, very large voltage and power fluctuations result due to the very large temperature ranges that occur in the automotive area, which may have variations between 0 K and 700 K in the temperature difference over the thermoelectric generator. Processing of these fluctuations by a d.c.-d.c. converter is possible, if at all, only in an inefficient manner.
The cost for the device in order to carry out the method in the motor vehicle is significantly lower due to the fact that the d.c.-d.c. converter is not necessary. In addition, the weight, required installation space, and complexity of the device are significantly less.
Multiple groups of modules electrically connected to one another in series are advantageously electrically connected to one another in parallel. This is particularly meaningful when not all of the modules of the thermoelectric generator are needed in order for the sum of their module open-circuit voltages to attain twice the predefined generator output voltage. If several of these groups of modules are present, whose sum of the module open-circuit voltages in each case attains twice the predefined generator output voltage, these groups may be connected in parallel in order to increase the output current intensity of the thermoelectric generator. In this way, all or at least as many of the modules of the thermoelectric generator as possible are usable at any time for generating electrical energy for the electrical consumer.
Advantageously, the module open-circuit voltages are measured and/or temperatures of the hot sides and/or the cold sides of the modules are measured, and on this basis the module open-circuit voltages are determined, and/or a temperature and a mass flow of a hot side medium and/or of a cold side medium are determined, and on this basis the module open-circuit voltages and/or the module open-circuit voltages are determined with reference to at least one predefined characteristic map. Input variables of the predefined characteristic map may be, for example, the determined temperatures of the hot sides and/or of the cold sides of the modules, and/or the determined temperature and the determined mass flow of the hot side medium and/or of the cold side medium, and/or parameters that are read from the control units of the motor vehicle. Output variables of the characteristic map may then be the module open-circuit voltages of the individual modules and/or connection defaults for the particular electrical connection of the modules. These options allow the quickest possible and precise determination of the module open-circuit voltages, and thus, rapid and dynamic adaptation of the electrical connection of the modules to changed conditions. This allows the modules to always be operated at their respective maximum performance point or at least close to the maximum performance point, even under conditions that change frequently and very dynamically, which occur in particular in a motor vehicle, for example in an exhaust system of the motor vehicle. Optimal energy-efficient utilization of the thermoelectric generator is thus made possible.
The device advantageously includes switches for electrically connecting the modules in order to allow rapid automatic electrical connection of the modules and thus an adaptation of the connection to the particular conditions acting on the thermoelectric generator. For a very small number of modules, for example only two modules, or for two relatively homogeneous groups of modules, for example, only one such switch, for example, would be necessary for electrically connecting the modules or module groups to one another either in series or in parallel.
The switches are advantageously designed as semiconductor switches to allow a cost-effective, simple, installation space-saving, and efficient implementation of the device. However, numerous other switches, such as relays, are also possible.
The device advantageously includes a processing unit for determining the module open-circuit voltages of the modules and/or for electrically connecting the modules corresponding to the determined module open-circuit voltages, i.e., for controlling the switches, for example the semiconductor switches. The processing unit is designed as a microcontroller, for example. This microcontroller is connected via driver stages, for example, i.e., via power switches, to the switches for electrically connecting the modules in order to control them.
In one advantageous embodiment, the device includes at least one sensor unit or a plurality of sensor units. By means of this sensor unit or the plurality of sensor units, for example module open-circuit voltages of the modules are directly measurable, and/or temperatures of hot sides and/or of cold sides of the modules are measurable, and/or a temperature and a mass flow of a hot side medium and/or of a cold side medium are determinable. Using the device with the method allows the particular module open-circuit voltages of the individual modules to be determined. Alternatively or additionally, the device may advantageously access characteristic maps, models, and/or parameters of the motor vehicle that are stored, for example, in control units of the motor vehicle, for example in an engine control unit, to thus determine an instantaneous state of the motor vehicle, its engine, for example, in particular to determine, for example, instantaneous exhaust gas temperatures and/or coolant temperatures and the instantaneous module open-circuit voltages of the modules over these temperatures.
Mutually corresponding parts are provided with the same reference numerals in all the figures.